1. Field of the Invention
The present invention relates to a method and an apparatus for making harmless a pollutant such as exhaust gases, polluted materials such as polluted water, polluted soil, etc.
2. Related Art
Serious social problems have occurred from pollution of the soils with dioxin-containing ashes produced by burning wastes, heavy metal-containing ashes, etc., pollution of rivers, lakes and marshes with waste acids, waste alkali or the like, pollution of underground water with factory waste liquids such as organic chlorine compound-based solvents including trichloroethylene, tetrachloroethylene, etc., pollution of soils with mercury, cadmium, lead, zinc, arsenic, cyan, chromium, copper, fluorides, or organic chlorine compounds, etc. The polluted water has been neutralized, and the polluted soil has been burnt or disposed of for land reclaiming.
However, the land reclaiming is disadvantageous, because it may cause new secondary pollution. There is also available a method by which the polluted soil is melted in a long time and then cracked (vitrified), but the method requires a long treating time and a high treating cost.
It is an object of the invention to provide a novel method and a novel apparatus for simply and economically treating the polluted materials in a short treating time.
The method for making harmless a material to be treated containing a pollutant, comprises the steps of arranging a pair of ejecting nozzles such that nozzle openings thereof are opposed to each other inside pressure-proof furnace, thermally treating that material, ejecting the thermally treated material through the nozzle opening of each of a pair of the nozzles into a space in the pressure-proof furnace, colliding the material ejected through one of the nozzles with that ejected through the other in the space inside the pressure-proof furnace and between a pair of the nozzle openings such that a portion of the pollutant of the material remaining non-decomposed by the thermal treatment may be decomposed.
The invention also relates to the apparatus utilizing this method or effecting this method.
That is, the apparatus for making harmless a material to be treated containing a pollutant according to the present invention, comprises a thermally treating unit for thermally treating said material, a pressure-proof furnace, a pair of ejecting nozzles arranged such that nozzle openings are opposed to each other inside a space in the pressure-proof furnace, and an ejector for ejecting the thermally treated material into said space through the nozzle openings of each of a pair of the nozzles, whereby the material ejected through one of the nozzles is collided with that ejected through the other in said space inside the pressure-proof furnace and between a pair of the nozzle openings such that a portion of the pollutant of the material remaining non-decomposed by the thermal treatment may be decomposed.
According to the present invention, the pollutant-containing material is first thermally treated to decompose the pollutant, and the material ejected through one of the nozzles is collided with that ejected through the other in the space inside the pressure-proof furnace and between a pair of the nozzle openings such that such pollutant of the material as remaining non-decomposed by the thermal treatment may be substantially decomposed. Thereby, the pollutant is made almost harmless. That is, if the material to be treated is ejected through the nozzle opening and collided with an external plate inside the pressure-proof furnace, the pollutant is decomposed owing to the kinetic energy and the thermal energy of the material ejected through the nozzle. However, considerably high temperature and pressure are required in this method in a case where the pollutant is a stable compound such as dioxin or PCB, for example. According to the present invention, since the materials are ejected through a pair of the opposed nozzles after being first thermally treated, and collided with each other such that such pollutant of the material as remaining non-decomposed by the thermal treatment may be decomposed. As a result, the highly stable compound such as dioxin or PCB can be decomposed by utilizing relatively low temperature and/or pressure.
According to the above nozzle/external plate utilizing method, high temperature and high pressure, for example 650xc2x0 C. and 300 atms (1 atm=1.01xc3x9710xe2x88x921 MPa), are required to entirely decompose dioxin only by heating under pressurizing. On the other hand, dioxin can be decomposed at far lower temperature and pressure according to the present invention as compared with that method.
For example, the first thermal treatment is effected at 1800xc2x0 C. to 2000xc2x0 C., and the temperature decreased from the first thermal treatment stage and the second colliding stage by around 20% of the original temperature, so that the thermally treated material is collided at the decreased temperature, for example under 25 atms (24 MPa) in the pressure-proof furnace. Therefore, when the material ejected through one of the nozzles is collided with that ejected through the other in the space inside the pressure-proof furnace and between a pair of the nozzle openings, the material reaches very high temperature and very high pressure so that such pollutant of the material as remaining non-decomposed by the thermal treatment may be substantially decomposed. The material to be collided may be in the form of a powder, a liquid or the like.
Preferably, a skirt portion is provided for each nozzle such that the each of the skirt portion is communicated with a nozzle opening at one end, and expanded toward the other remote end, and openings of the skirt portions at the other remote ends opposite to the nozzle openings are opposed to each other to sandwich a space therebetween where the materials from the nozzles collide with each other. The skirt portion may be in the form of a conically spread shape as viewed in an ejecting direction. The material to be treated is ejected through the nozzle, restrained with the skirt portion, and led to the colliding space. In this manner, the energy at the collision is remarkably concentratedly increased by the utilization of the skirt portions. The energy usable on collision is confined or concentrated, in a limited area, to a very high level as in the case of an ejection outlet of a rocket by the provision of the skirt portions.
When a gas at a relatively low pressure is flown along the inner peripheral surface of the skirt portion, i.e., between the material ejected through the nozzle opening and the inner peripheral surface of the skirt portion, a so-called curtain can be formed along the inner peripheral surface of the skirt portion to prevent the material from being scattered.
Preferably, a hollow cylindrical member is provided to surround the space where the materials to be treated collide with each other, and the cylindrical member is rotated during when the materials are being collided with each other. By so doing, the cylindrical member functions as a wind shield against shock waves generated on collision, reduces the pressure inside the cylindrical member and minimizes collision influences upon the surrounding area. The pressure at that time can be further reduced by providing a caterpillar inside the cylindrical member.
The material to be treated is preferably thermally treated before being fed to each nozzle. This thermal treatment is particularly efficient in that most of, for example, 90% or more of the pollutant is decomposed and the material is decomposed at almost 100% on collision.
The harmful material is not limited, and may include harmful organic compounds, harmful inorganic compounds and harmful microorganisms (pathogens). As the harmful organic compounds, recitation may be made of organic solvents (particularly chlorine-based organic solvents), organic chlorine compounds such as trichloroethylene, tetrachloroethylene and dioxin, organic bromine compounds, and harmful gases (yperite, sarin, tabun, phosgene, etc.), for example. As the harmful microorganisms, particularly, pathogens of biohazard levels III and IV may be recited. The material to be treated are not limited. The present invention can be applied to any pollutant-containing materials to be treated, excluding metals themselves, in any forms, such as polluted air, polluted soil, tires, plastics, medical wastes, shredder dusts, construction wastes, heavy metal-containing ashes, etc.
According to the present invention, the collision between the materials to be treated decomposes the pollutant in the material and thereby makes the pollutant harmless. Further, when the materials containing the pollutant such as heavy metal are collided with each other, the material is solidified into a slag or glassy sold matter. Thereby, the pollutant can be made harmless through being enclosed in the thus formed solid.
These and other objects, features and advantages of the invention will be appreciated upon reading the following description of the invention when taken in conjunction with the attached drawings, with the understanding that some modifications, variations and changes could be easily made by the skilled person in the art to which the invention pertains.